Pressure sensors comprise a platform, a measuring membrane and a transducer, wherein the measuring membrane is secured on the platform, wherein the measuring membrane is contactable with at least one pressure and has a pressure-dependent elastic deformation, and wherein the transducer provides an electrical signal dependent on the deformation of the measuring membrane, wherein the platform, furthermore, has a membrane bed, on which the measuring membrane lies in the case of overload, in order to support the measuring membrane.
In such case, it is advantageous that the membrane bed has a contour approximating the natural pressure-dependent deformation, i.e. a contour matching that of the so-called deflection curve. It is difficult, however, to manufacture such a membrane bed in a reproducible and cost-effective manner.
The shaping of the bed as well as its manufacture depend on the material of the membrane bed and of the substrate, which bears the membrane bed, and what sort of joining technology is selected for joining the platform or the membrane bed with the membrane.
Especially suitable for pressure difference sensors are Si platforms, since these withstand the static pressure well. There exist various methods for connection of two silicon chips, such as, for example eutectic bonding or silicon direct bonding. In view of the requirements for a hermetically sealed and fixed connection of the components, which, in spite of this, has no major after-effects, these bonding methods according to the state of the art deliver a yield and reproducibility, which is still capable of improvement. Additionally, the manufacture of, for example, spherically concave beds according to U.S. Pat. No. 7,360,431 B2 of YAMATAKE is not directly possible in silicon. Currently known are either the non-established methods of gray scale lithography or a direct grinding/polishing of the silicon, which leads to reproducible results only with great effort.
The yet unpublished patent application DE 102008043171 discloses a pressure sensor comprising at least one platform, at least one measuring membrane and a transducer, wherein the measuring membrane comprises a semiconductor material (especially silicon), wherein the measuring membrane, enclosing a pressure chamber, is secured to the platform, wherein the measuring membrane is contactable with at least one pressure and is elastically deformable in a pressure-dependent manner, wherein the transducer provides an electrical signal dependent on the deformation of the measuring membrane, wherein the platform has a membrane bed, against which the measuring membrane lies in the case of overload, in order to support the measuring membrane, characterized in that the membrane bed has a glass layer, whose surface faces the measuring membrane and forms a wall of the pressure chamber. The surface of the glass layer is especially provided with a contour, which is suitable for supporting the measuring membrane in the case of overload. For this, the surface of the glass layer can be micromechanically processed. The glass layer can likewise have a surface contour, which is prepared by means of hot embossing. Furthermore, this patent application discloses that it is advantageous that the membrane bed has a surface contour, which is approximately the same as the deflection curve of the measuring membrane, or equals such.
Although this procedure leads to satisfactory results as regards the quality of the membrane beds, alternatives to the pressure sensors manufactured in such a way are still desired.